Balloon catheters are widely used in the medical profession for various intraluminal procedures. One common procedure involving the use of a balloon catheter relates to angioplasty dilation of coronary or other arteries suffering from stenosis (i.e., a narrowing of the arterial lumen that restricts blood flow). Although balloon catheters are used in many other procedures as well, coronary angioplasty using a balloon catheter has drawn particular attention from the medical community because of the growing number of people suffering from heart problems associated with stenosis. This has led to an increased demand for medical procedures to treat such problems. The widespread frequency of heart problems may be due to a number of societal changes, including the tendency of people to exercise less while eating greater quantities of unhealthy foods, in conjunction with the fact that people generally now have longer life spans than previous generations. Angioplasty procedures have become a popular alternative for treating coronary stenosis because angioplasty procedures are considerably less invasive than other alternatives. For example, stenosis of the coronary arteries has traditionally been treated with bypass surgery. In general, bypass surgery involves splitting the chest bone to open the chest cavity and grafting a replacement vessel onto the heart to bypass the blocked, or stenosed, artery. However, coronary bypass surgery is a very invasive procedure that is risky and requires a long recovery time for the patient.
To address the increased need for coronary artery treatments, the medical community has turned to angioplasty procedures, in combination with stenting procedures, to avoid the problems associated with traditional bypass surgery. Typically, angioplasty procedures are performed using a balloon-tipped catheter that may or may not have a stent mounted on the balloon (also referred to as a stented catheter). The physician performs the angioplasty procedure by introducing the balloon catheter into a peripheral artery (commonly one of the leg arteries) and threading the catheter to the narrowed part of the coronary artery to be treated. During this stage, the balloon is uninflated and collapsed onto the shaft of the catheter in order to present a low profile which may be passed through the arterial lumens. Once the balloon is positioned at the narrowed part of the artery, the balloon is expanded by pumping a mixture of saline and contrast solution through the catheter to the balloon. As a result, the balloon presses against the inner wall of the artery to dilate it. If a stent is mounted on the balloon, the balloon inflation also serves to expand the stent and implant it within the artery. After the artery is dilated, the balloon is deflated so that it once again collapses onto the shaft of the catheter. The balloon-tipped catheter is then retracted from the arteries. If a stent is mounted on the balloon of the catheter, the stent is left permanently implanted in its expanded state at the desired location in the artery to provide a support structure that prevents the artery from collapsing back to its pre-dilated condition. On the other hand, if the balloon catheter is not adapted for delivery of a stent, either a balloon-expandable stent or a self-expandable stent may be implanted in the dilated region in a follow-up procedure. Although the treatment of stenosed coronary arteries is one common example where balloon catheters have been used, this is only one example of how balloon catheters may be used and many other uses are also possible.
One problem that may be encountered with conventional angioplasty devices and techniques is the proper dilation of stenosed regions that are located along a curved section of a lumen, at a junction of a small branch vessel with a significantly larger primary vessel, and/or across branching regions of a vessel. Existing devices may distort or even damage the vessel wall defining the body lumen (e.g., arterial wall). The behavior of an angioplasty balloon is largely dictated by its compliance. A balloon made of low-compliance material(s) generally tolerates high inflation pressures and attains a uniform predictable diameter even when some parts of the surrounding artery contain areas of severe stenosis and dense calcification that resist dilatation. A potential drawback is that a low-compliance balloon always straightens as it expands, regardless of the shape of the surrounding artery. If such a balloon is being used to drive the expansion of a stent, the shape of the balloon, a straight cylinder, is imposed on the shape of the stent. The presence of a straight stent in a curved artery causes stresses and strains that damage either the stent or the artery.
Both effects can lead to arterial microtrauma, hyperplasia and restenosis, especially if the vessel is moving (for example, with the cardiac cycle in the case of a coronary stent, with respiration in the case of a renal stent, or with movement of the thigh and leg in the case of a superficial artery stent). Balloons made of high-compliance materials face a different set of problems which often made them unsuitable for high-pressure angioplasty of unyielding lesions. A compliant balloon expands into whatever low resistance space is available, such as the lumen of the artery upstream and downstream of the lesion and areas of weakness in the arterial wall. High-pressure inflation of a high-compliance balloon may cause potentially damaging inflation of non-diseased segments of the artery, and rupture of a weak segment. Lower pressure inflation leaves many of the more severe lesions untreated. In addition, a high-compliance balloon may fail to provide the force needed to expand a stent in areas of arterial disease, particularly when the diameter is small and higher inflation pressures are required to general sufficient wall tension.
The embodiments described below may be useful in treating stenosed regions along curved vessel regions, along branched vessel regions, and at or near vessel junctions. The claimed embodiments may also solve other problems as well.
It may be desirable to provide a balloon that includes discrete circumferentially-restrained regions, as well as including an ability to provide for longitudinal expansion while not exceeding a predetermined outer diameter.